This invention relates to a method and apparatus for selective coring or drilling, with particular application to recovering core samples from potential water, oil or gas reservoirs.
Extracting core samples from downhole wells is an important aspect of the drilling process to provide geological and geophysical data to establish reservoir models.
Conventionally, core samples of a borehole are recovered from the bottom of a borehole during the drilling phase by means of a bit attached to the lower end of a core barrel which is further attached to the lower end of the drill string.
Sidewall cores may also be recovered during or after the logging phase, and a known method for obtaining side wall cores is described in our UK Patent No 2305953B. The conventional method of recovering borehole core samples typically produces long undisturbed samples which are preferred to the short, often highly fractured samples produced by the sidewall coring method, and it is desirable to increase the quality of the sidewall samples.
The accurate positioning of known coring apparatus is also difficult, frequently resulting in samples of limited value being recovered from geological zones of little interest.
Moreover, the equipment currently available to remove sidewall core samples tends to be somewhat cumbersome and expensive.
A further limitation of the prior art is the method of piercing the well bore lining to allow ingress of production fluids. Wells are conventionally lined with a section of metal tubing which is perforated to allow fluid to enter into the borehole.
These perforations are normally formed in a violent manner by setting off an explosive charge to fire projectile(s) through liner or by the explosive charge itself being designed to blast through the material. The lining is thereby ruptured and perforations are thus formed. However, such a method results in compression of the rock formation surrounding the perforation, reducing its pore size and creating a local barrier to fluid flows around, and significantly, into the borehole. The lining rupture caused by the explosive charge is also relatively uncontrolled and creates a random shape which is not streamlined and requires higher fluid energy to negotiate the perforation.
According to a first aspect of the present invention there is provided apparatus for creating a hole in a subsurface formation. The apparatus includes an inner assembly adapted for connection to an elongate member. The inner assembly is adapted to be raised and lowered within a borehole. The inner assembly includes a member capable of engaging either an outer assembly or the borehole.
According to a second aspect of the invention there is provided a method for creating a hole in a subsurface formation. The method comprises the steps of:
connecting an inner assembly to an elongate member, said inner assembly including a member capable of engaging either of an outer assembly or a borehole;
lowering the inner assembly within the borehole;
engaging the member with either of the outer assembly or the borehole to resist substantially vertical movement of at least a portion of the inner assembly with respect to at least one of the outer assembly or the borehole; and;
driving a cutting member into said subsurface formation to create a hole.
Preferably, the method is performed using the apparatus according to the first aspect of the invention.
The subsurface formation may be a casing, liner or subterranean formation.
Preferably, the method further comprises drilling a hole in a casing of a borehole, typically prior to drilling a hole in the subterranean formation.
The cutting member may be a drill bit. Preferably, the drill bit engages the lining of the borehole at a point proximate to the producing zones. Alternately or in addition, the drill bit preferably engages the borehole and punctures a hole therein.
In one embodiment the inner assembly also comprises a coring barrel.
A rotation resistance mechanism is preferably further provided to prevent rotation of at least a portion of the inner assembly with respect to at least one of the outer assembly or borehole.
Preferably, the member capable of engaging either the outer assembly or the borehole is an expandable member.
Preferably the outer assembly is incorporated into a tubular string comprising a side exit mandrel. Preferably the outer assembly is secured in said borehole before the inner apparatus is lowered therein. Typically, the tubular string is a drill string.
Preferably the expandable member engages the outer assembly. Preferably the expandable member is an inflatable member. Typically the expandable member is formed from rubber and metal and preferably has a high friction coefficient.
Preferably the inner assembly comprises a piston cylinder and preferably a piston rod member. Preferably the piston rod member extends through the piston cylinder, then typically through a rotation resistance mechanism and may connect to spacers below the rotation resistance mechanism. The coring barrel is preferably connected to the lower (opposite) end of the spacers if used or the rotation resistance mechanism if no spacers are used. Typically a drill bit is connected to the coring barrel to engage the geological formation.
Preferably, the rotation resistance mechanism comprises a locking mechanism which locks the piston rod member in a rotational direction with respect to the piston cylinder.
Preferably the elongate member is attached to a wireline head. Preferably the wireline head comprises a sacrificial weak link between the elongate member and the wireline head. Preferably the elongate member comprises electrical conductors and cable. Preferably the electrical conductors transfer communication and/or power from the surface of the borehole to the wireline head, or from the wireline head to the surface.
Preferably the wireline head is attached to a housing. Preferably the housing comprises a valve block, a hydraulic pump, power pack and fluid reservoir. Preferably the housing is also attached to the piston rod member.
Preferably the power pack comprises an electric motor, most preferably a low amperage electric motor. Preferably the electric motor is connected to electrical conductors of the elongate member. Preferably the housing also has an electronics carrier which is also attached to electrical conductors of the elongate member. Typically, the elongate member is a wireline.
Preferably the motor is activated from the surface, through the electrical conductors, to drive the hydraulic pump to transfer fluid from the reservoir into the piston cylinder.
Preferably the cylinder and inflatable member are connected by two fluid flow control means which may be valves. Typically, one valve permits fluids to transfer from the cylinder to the inflatable member and the second valve permits fluids to travel in the opposite direction, that is from the inflatable member to the cylinder. Typically either valve may be closed to resist transfer of fluids. Optionally the valves may be opened by actuation thereof, or alternatively when a specified fluid pressure is attained.
Preferably the main hub part of the piston cylinder is separated into two portions, typically by a piston attached to the piston rod assembly.
Preferably fluids can be injected or rejected from each portion of the main hub part of the piston cylinder. Preferably a first hydraulic line connects to the first, upper, portion of the main hub part of the piston cylinder and a second hydraulic line connects to the second, lower, portion of the main hub part of the piston cylinder. Typically each hydraulic line connects to the hydraulic pump and fluid reservoir. Typically fluid flow control means are provided to control the fluid travelling in the hydraulic lines between the reservoir/pump and each portion of the main hub part of the piston cylinder. Preferably the rate and direction of the fluid may be controlled by the fluid control means. Preferably the fluid control means are valves. Preferably there are four valves.
Preferably the first valve is provided on the first hydraulic line. Preferably the first valve is a two way valve, that is it may be set to allow fluid to travel from the reservoir to the cylinder or in the opposite direction, from the cylinder to the reservoir.
Preferably the second hydraulic line connects to the reservoir and pump via the other valves which are connected in parallel. Typically the second valve may transfer fluid from the reservoir to the lower portion of the cylinder. Typically the third and fourth valves allow fluid transfer from the lower portion of the cylinder to the reservoir. Preferably the third valve can accurately regulate the amount of fluid passing therethrough. Typically, a further valve is provided in series with the third valve to resist the flow of fluid therethrough below a specified pressure.
Typically, each valve can be set to resist flow of fluids therethrough.
Preferably the inner assembly has drive means for rotating said core barrel about its longitudinal axis. Preferably the drive means comprises a hydraulic motor, most preferably a positive displacement drilling motor or mud motor.
Preferably the inner assembly comprises flow diverter means, and most preferably the expandable member functions as the flow diverter means.
Preferably a rod assembly comprises the housing containing the power pack which comprises the hydraulic pump, electrical motor, electronics carrier and reservoir; and typically the rod assembly further comprises the piston rod member, piston, spacers (if used), mud motor, coring barrel and drill bit.
Preferably a packer assembly comprises the piston cylinder, the rotation resistance mechanism and the member capable of engaging the borehole or outer assembly.
The inflatable member may be inflated by injecting pressurised hydraulic fluid therein which expands and engages the borehole or outer assembly.
Preferably the expandable member frictionally engages the borehole or outer assembly, insodoing providing a reaction force for said coring barrel to engage an oil and gas reservoir below.
Preferably, fluid is injected into the piston cylinder of the inner assembly to move the piston with respect to the upper portion of the piston cylinder, thereby moving the rod assembly with respect to the packer assembly. The rod assembly includes the coring barrel and is thereby pushed down towards the oil and gas reservoir below wherein the reactive force is typically provided by the expandable member engaging the outer assembly.
Preferably the inflatable member is then disengaged from the outer assembly by appropriate means e.g. deflation of the member.
Typically the rod assembly is held by the wireline, and the piston and the top of the piston cylinder are pushed together by injection of hydraulic fluids which enter the lower portion of the piston cylinder thereby moving the packer assembly downhole.
In this position the rod and packer assembly are typically in the start position with respect to each other; but lower (e.g. 5 ft) with respect to the borehole, than the position in which they started collecting the core sample.
The method may be repeated as many times as necessary to complete the core sample. Typically the length of the main hub part of the piston cylinder is 5 ft, but could suitably be longer or shorter. Typically the length of the core barrel is 25 ft, but could suitably be longer or shorter. Therefore the method will normally be repeated five times, although this may be varied depending on the cylinder size, core barrel size, length of core required or for other reasons.
To extract the inner assembly from the borehole, the expandable member may be disengaged and the inner assembly may be winched up to the surface. Alternatively where winching cannot retrieve the inner assembly, because, for example, the coring barrel is jammed in the geological formation, the method of coring may be adapted to remove the inner assembly from the borehole.
In such a case, the expandable member may engage the borehole or outer assembly. Hydraulic fluid is injected into the lower portion of the cylinder to push the piston and complete rod assembly in an upwards direction. Optionally, the winch may also be used to assist this operation.
Preferably, the expandable member then disengages the borehole and the inner assembly is held on the wireline. The rod and packer assembly may then be separated by injecting hydraulic fluid into the upper portion of the piston cylinder, causing the packer assembly to move in an upwards direction.
The rod assembly may then be raised by engaging the expandable member with the outer assembly and injecting pressurised fluid into the lower portion of the cylinder, forcing the piston and rod assembly in an upwards direction.
This process may be repeated as necessary until the inner assembly may be retrieved by winching alone.